Gas analysis apparatus



June 13, 1944.' w, A M'cMlLLAN 2,351,532

GAS ANALYSIS APPARATUS Filed NOV. 9, 1940 WALLACE A. Mc MlLLAN INVENTOR Patented June 13, 1944 2,351,532 GAS ANALYSIS APPARATUS Wallace A. McMillan,

by mesne assignmen New York. N. Y., a corpo Forest Hills, N. Y., assignor,

ts, to 'The Texas Company,

ration of Delaware Application November 9, 1940, Serial No. 364,996

(Cl. 23Z54) 2 Claims.

This invention relates to gas analysis and more particularly to a method and apparatus tor quantitatively determining the percentages of gaseous olefins and parafns in a gaseous mixture containing the same.

In the past quantitative analysis of gaseous mixtures has frequently been accomplished by passing these mixtures through various absorption mediums which are active to absorb one or more constituents of the mixture whileremaining inactive to absorb other constituents thereof. Although this method may be generally satisfactory for analyzing certain gaseous mixtures, it is not accurate for other gaseous mixtures since it is frequently impossible to n'd reagents which will absorb one of the constituents to substantial completion without at the same time absorbing any appreciable quantity. of another constituent. This is particularly true in the analysis of hydrocarbon gases containing both parain hydrocarbons and oleiins. An absorption analysis of this type also requires much time and is generally diicult due to the handling of the gaseous mixture in passage through a number of absorption reagents.

The principal object of the present invention is to provide a method of and apparatus for analyzing a gaseous mixture which is quantitatively accurate, and which may be readily carried out With'a minimum of time consumption and o equipment. Another object of the invention is to provide a method and apparatus for quantitatively analyzing a complex mixture of gases such as a gaseous hydrocarbon mixture obtained from oil refineries or other by-product gases, including complex mixtures of hydrocarbon gases containing both saturated and unsaturated hydrocarbon constituents.

In my copending patent application Serial No. 359,853, iiled October 5, 1940, I have disclosed an apparatus for theprecise analytical distillation and fractionation of gaseous mixtures in which a distilling bulb is surmounted by an elongated fractionating column having a partial condenser at its upper end, the column having an oiftake leading to receivers, each of which is adapted to receive and hold a mixture of vapors produced by the fractionation. Automatic regulation of the distillation is provided and the apparatus also includesequipment forautomatically recording the temperatures'of fractionation and the pressures of the vapors passed to the various receivers.

In the U. S. Patents Nos. 2,147,606 and 2,147,607 tolwcMillan et al. granted February 14, 1939, a

methodand an apparatus are disclosed for analyzing mixtures oi .gases such as hydrocarbon gases containing both saturated and unsaturated hydrocarbon constituents. As described in those patents, a sample of the gaseous mixture to be analyzed is confined within a closed system, wherein the gas volume can be measured under regulated conditions of temperature and pressure. Another gas which is chemically reactive with a constituent or constituents of the mixture to be analyzed is added to that mixture and the volume oi' the added gas is determined. The mixture of gases is then passed through a treating zone, as in Contact with a catalyst, until substantially complete reaction of the known gas with. the constituent or constituents oi the gaseous mixture takes place, resulting in a change or reduction in total volume of the gases. The volume of the reacted gases is then measured and from this the proportion of the constituent or constituents of the gaseous mixture may be4 computed.

In accordance with the present invention, a sample of a gaseous mixture is fractionated and the cuts are passed to suitable receivers, one or more of which may'then contain a mixture of hydrocarbons which could not bev separated by fractional distillation such as, for instance,

propylene and propane.. The volume of the mixture of gases in such a receiver is measured, after which a known amount oi hydrogen is added to the receiver. The mixture is then passed back and forth over a hydrogenation catalyst until there is no further decrease in the volume of gases. The diierence between the volume of the mixture before and after hydrogenation is a direct measure oi the olefin content of the mixture. Apparatus is provided for the fractional distillation and for automatically circulating the gaseous mixture back and forth over the catalyst.

For a better understanding oi the invention,

reference may be had to the'accompanying drawing in which:

Figure 1 is an elevational view, generally diagrammatic, of an apparatus embodying the improvements of the invention and,

Figure 2 is an elevation showing a modified form of part of the apparatus for circulating the mixture.

Referring to the drawing, a distillation bulb III is surmounted by an elongated f-ractionating tube l2 or smalldiameter, which tube is provided 'with a vacuum jacket N5. The bulb il) may be surrounded with a thermos bottle for low temperature work and the upper end of the tube or co1- ingfrom the conduit 22 to 'another receiver, not

shown, and the conduit 22 preferably extends to a suitable vacuum pump 32 which is adapted to evacuate the entire unit. It is to be understood that any number of receivers maybe connected to the manifold or conduit 22, depending on the number of fractions it is desired to separate from the sample by fractional distillation. 'I'he pressure of distillation is controlled by a suitable adjustable rate valve 34 which may be manually controlled as disclosed in my U. S. -Patent No. 2,005,323'granted June 18, 1935 or automatically adjustable as disclosed in my aforementioned copending application Serial No. 359,853, and is measured by a manometer 36 communicating with the conduit 22 between the valve 34 and the fractionatingcolumn I2.

In operation of the apparatus thus far described, a sample of the gas to be analyzed is supplied to the bulb I8 through the valved tube 38-and is pre-cooledin any suitable manner, such as by immersing the bulb .in a thermos flasklr4 containing liquid air or other suitable cooling medium. The rst fixed gas cut is then collected in one of the receivers 24 for further analysis. A controlled heating of the sample then eiects distillation of the liquifled portion, the vapors passing upwardly through the column I2, a portion of the vapors 'being condensed by partial condenser I 8, thereby providing reflux for the column which travels down the tube I2 counter-current to the upnowing vapors'. The sharp 'fractionation thereby obtained enables the separation of constituentsof the mixture, according to their boiling points, the temperature of distillation being measured by a suitable thermocouple (not shown) positioned in the upper portion of the column I2.A As long as one constituent or compound of the mixture is being vaporized, the distillation temperature will remain substantially constant and during this time the distilled vapors will be collected in one of the receivers 24.

In complicated hydrocarbon mixtures containing both saturated and unsaturated hydrocarbons, it may not prove possible to separate certain saturated or unsaturated hydrocarbons having approximately the same boiling points, such as propylene which boils at -41 C., and propane, boiling at -42 C., the result of which is that the distilled vapor accumulated in one or more of the receivers 24 may still be a mixture of two or more hydrocarbons. In order to measure the olefin content of a mixture of this kind the method and apparatus now to be described is provided.

The pipe 26 leading to the receiver 24 has connected thereto'a suitable manometer 48 capable of measuring the volume of the mixture of gases, such as propylene and propane, in the receiver 24.. Also communicating with the pipe 28 is another pipe 42 containing a valve 44 and leading to a catalyst tube 48 formed in the shape of an in- Iverted U and adapted to be filled with a catalyst to be described hereinafter. A pipe 48 connected to the other leg of the catalyst tube ,46' leads downwardly to a container, such as the bulb 58, preferably arranged at a'. level below the lower` end of the receiver 24. The pipe 48 is provided with a check valve 52 adapted to prevent flow of gases downwardly through the pipe. A pipe 64 connects the lower end of the receiver 24 to the pipe 48 through another pipe 56 containing a check valve 58 adapted to prevent flow of gases toward the receiver 24. Another container or bulb 68 is connected to the bulb 50 by means of a barometric U tube connection 62 and is disposed at a slightly higher elevation than the bulb 50. The bulbs 58 and 68 and the tube 62 are adapted to contain a liquid such as mercury, and in order to prevent the mercury from passing upwardly in the pipe 48, a liquid valve ,64 is provided of a type similar to that disclosed in my U. S. Patent 2,085,323, granted June 18, 1935. This valve preferably comprises a disc of sintered glass held in' the pipe 48 by suitable means such as a pair of flanges or a direct seal as disclosed in my copending application Serial No. 359,853. 'I'he sintered glass disc being porous is constructed so as to be permeable to vapors but impervious to mercury. Gases may, therefore, pass downwardly into the bulb 58 but the mercury will not be able to pass upwardly in the pipe 48 above the valve 64. A source of hydrogen is adapted to be connected to the receiver 24 through a suitable connection containing a valve 66. After the volume of the gases in receiver 24 are measured by means of the manometer 48, hydrogen is added to the receiver through the pipe 64 andthe volume of the mixture of gases then in the receiver is measured by noting the pressure increasev on the manometer 48. The mixture of hydrogen and olefin containing gas-ls then circulated back and forth through the catalyst tube -46 by means` of the following equipment. 'I'he bulb 68 is connected by means of a pipe 68 containing a valve 18 to aUshaped tube 'I2 having an enlarged closed portion 14 and an open end 16. A source l of vacuum is adaptedto be connected to thepipe 68 through a tube containing a valve 'I8 and a source of air pressure may, if desired, be connected to the pipe 68 through the valve 88. A valve 82 in the pipe 68 serves to connect this pipe with the vacuum or the air supply. Leading from the tube 12 is another tube 84 containing an inverted U-shaped portion 86. connected in turn to an open-topped tube 88the lower end of which is connected through conduit 88 to the portion 14 of the tube 12.

The operation of this apparatus is as follows: Vacuum is applied through valves 18 and 82 to the pipe 68, whereupon mercury will risein the bulb 68, in the closed leg of the tube 12 and in the tube 88 until the mercury in tube 98 syphons into the top of the member 1.4, whereupon air will enter through the open-topped tube 88. The mercury will then drop in bulb 68 and in the closed leg of the tube 12 until a point is reached in the open leg of tube 12 where the mercury will syphon back in to the tube 88. The bottom of the tube 88 will thus be sealed oil and the vacuum cycle will be restored. As the mercury rises in bulb 68, it will, of course, drop correspondingly in the bulb 68, which results in gas passing from the receiver 24 through the check valve 58 and the porous valve 64 into the bulb 68. 'When the catalyst in the tube I46 and back into the receiver 24. This operation will continue substantially automatically and after sulcient hydrogenation has taken place the volume of the mixture will reach a constant minimum which can be measured by means of the manometer lill.V The difference between this volume and the volume of the mixture of hydrogen and olefin containing gas before hydrogenation will be a direct measure of the oleiin content of the gas sample.

Although any suitable hydrogenation catalyst may be embodied within the tube or chamber Mi, it is preferred that a catalyst be used which is effective at atmospheric temperatures. For this purpose very satisfactory results have been secured with catalysts selected from reduced nickel, cobalt and platinum. By way of example, the preparation oi such a reduced nickel catalyst is herein described. An amount of shredded, longi-lbre asbestos is digested with hot nitric acid, after which it is washed, dried and ignited. The asbestos is then transferred to a clean procelain evaporating dish to which is added a quantity of C. P, nickel nitrate hexahydrate. Suihcient boiling distilled water is added to the mixture to allow' the asbestos to become thoroughly saturated with the solution on stirring, after which an amount vof C. P. concentrated ammonium hydroxide is added to the mixture and the mass thoroughly stirred to a thick paste. The dish should be covered and allowed to dry as much as possible on a steam bath. The final drying is accomplished in van oven at 105 C. for about eight hours, after which the dry mass is then broken up with a glass rod and packed in the U tube to be used for the catalyst'chamber. Both ends of the tube are then plugged loosely with ignited asbestos or glass wool and the tube is then heated to a temperature of about 310 C. While air is pulled through it. `This is continued until no further brown fumes are evolved and the whole mass has become entirely black. The tube is then cooled and connected t the apparatus as shown in Figure 1 and preferably flushed out with hydrogen applied through the valved connections 92 and 96, the valves 44 and 96 remaining closed. After flushing with hydrogen the tube du is then preferably heated for several hours as by placing an electrical heater over and around the same, the temperature not exceeding about 325 C., while a current of hydrogen is still passing through the tube. of air the catalyst will be ready for use.

Other systems than the one shown could be used for oscillating the gases through the catalyst. As shown, for instance, in Figure 2, an electrical contact 98 can be mounted in the pipe t8 directly above the bulb 60' and this contact can be included in an electrical circuit comprising wires |00, |02, the solenoid |04 and a source of electrical supply |06. The circuit will be completed from the electrical source |06 to a point in the tube 62',

solenoid |04 is connected to the operating arm |08 of a valve ||0 in a line between the source of vacuum ||2 and the pipe |58'.v Assuming the valve is held in its open position by means of a tension spring lll, the vacuum .from H2 will be applied through the pipe 68 and the mercury will rise in bulb 60 until it makes contact with the member 98, whereupon the electrical circuit will be completed so that the solenoid |04 will close the valve ||0, thus shutting off the vacuum. The valve ||0 is preferably provided which will be constantly sub-f merged in the mercury. The armature of the When cooled in the absence with a vent, not shown, by means of which the pipe 08' will be connected to atmosphere when thevalve is in its closed position. The mercury will then drop in the bulb 60', thereby opening the electrical circuit and allowing spring IM- to open the valve ||0 at which the cycle will be repeated.

It is understood that the apparatus which has been described can be applied to one or all of the receivers 24. if desired, the means shown to the right of valve 82 .in Figure 1 may be connected through pipes H0 and ||8 to additional bulbs 60 arranged to oscillate the gases back and forth from other receivers over their respective cata- 15 l lysts.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

l1. Apparatus for quantitatively determining the percentages of gaseous unsaturated and saturated hydrocarbons in a gaseous mixture containing the same, comprising a receiver 'for said mixture, a conduit connected to the receiver whereby a known volume of hydrogen may be introduced therein, a bulb adapted to contain mercury, a conduit connecting said bulb and said receiver and containing a hydrogenation catalyst, a second conduit connecting said bulb and said receiver and means for automatically and-intermittently drawing the mixture of the hydrogencontaining gases from said receiver into said bulb through said second conduit and then returning the mixture through said catalyst to saidreceiver through the first-mentioned conduit, said.

last-mentioned means comprising a U tube closed at one end, said end being'connected to said bulb, a tubular container having its upper end open and its lower end connected to the closed end of said U tub/e, an inverted U tube connected at one end to the open leg of said rst Uv tube and at the other end to said container, said container, said U tubes and said bulb normally holding a quantity of mercury, a source df vacuum connected to the closed end of said iirst mentioned U tube, the arrangement being such that the vacuum will draw mercury from said bulb and from said container so as to draw gases from the receiver into the bulb, whereupon air will enter through the open end oi said container to break the vacuum, thus allowing mercury to return to said bulb, forcing the gases through the catalyst and back into said receiver, and a :nanometer communieating with said receiver for indicating thevvolurne of hydrogen-containing gases in said receiver before and. after said gases are passed through said catalyst.

2. Apparatus for quantitatively determining the percentages of gaseous oleiins and parains in a gaseous mixture containing the same, comprising a receiver adapted to hold said mixture, a conduit connected to said receiver whereby a known volume rof hydrogen may be introduced therein, a conduit connected to the upper and lower ends of said receiver, aquantity of a yhydrogenation catalyst in said conduit, a pair of oppositely opening checkA valves in said conduit, and means for intermittently withdrawing a portion of the hydrogen-containing gaseous mixture,

with said conduit between said check valves, a quantity of mercury in said vessel, a second vessel disposed at a higher elevation than said first vessel, a tube connecting said vessels, means for intermittently applying a vacuum to said second vessel whereby mercury is alternately'drawn into said second vessel from said first vessel and then gravitated back to said first vessel, said lastnamed means comprising a vacuum'siphon, a manifold connecting said siphon to saidI second vessel,4 a source of vacuum connected to said manifold, and a :nanometer communicating with Y said receiver for measuring the volume of hydrogen-containing gases in said receiver before and after said gases are passed through said catalyst.

' WALLACE A. McMIILAN. 

